1. Field of the Invention
The Present invention relates to a plasma display panel, and more particularly to an energy recovery apparatus and method for a plasma display panel.
2. Description of the Background Art
A plasma display panel (hereinafter, referred to as “PDP”) displays a video image by adjusting a gas discharge period of each of pixels according. to digital video data. As a representative example, there is a PDP with three electrodes, driven by an alternating current (AC) voltage as shown in FIG. 1
Referring to FIG. 1, a discharge cell of a tri-electrode AC surface discharge PDP includes a scan electrode 28Y and a sustain electrode 29Z formed on an upper substrate 10, and an address electrode 20X formed on a lower substrate 18.
The scan electrode 28Y and the sustain electrode 29Z respectively include transparent electrodes 12Y and 12Z, and metal bus electrodes 13Y and 13Z that have a narrower width than the transparent electrodes 12Y and 12Z and that are formed at one end of each of the transparent electrodes 12Y and 12Z. The transparent electrodes 12Y and 12Z formed on the upper substrate 10 use Indium-Tin-Oxide (ITO). The metal bus electrodes 13Y and 13Z formed respectively on the transparent electrodes 12Y arid 12Z use metal such as chrome (Cr) and serve to reduce voltage drop caused by the transparent electrodes 12Y and 12Z with high resistance. An upper dielectric layer 14 and a protection film 16 are sequentially formed on the upper substrate 10 on which the scan electrode 28Y and the sustain electrode 29Z are formed. The upper dielectric layer 14 is accumulated with electric charges generated during the plasma discharge. The protection film 16 protects the upper dielectric layer 14 from sputtering generated during the plasma discharge and increases the emission efficiency of secondary electrons. Magnesium oxide (MgO) is usually used as the protection film 16.
The address electrode 20X is formed in such a manner that it intersects the scan electrode 28Y and the sustain electrode 29Z. A lower dielectric layer 22 and barrier ribs 24 are sequentially formed on the lower substrate 18 on which the address electrode 20X is formed. A phosphor layer 26 is coated on the lower dielectric layer 22 and the barrier ribs 24. The barrier ribs 24 are formed in parallel to the address electrode 20X to physically demarcate the discharge cell, and prevent ultraviolet rays and visual rays generated during the discharge from leaking toward neighboring discharge cells. The phosphor layer 26 is excited and emitted by ultraviolet generated during the plasma discharge and emits one of visual rays, i.e., red, green and blue. A mixed gas of inert gases, such as He+Xe, Ne+Xe or He+Xe+Ne, is injected into discharge spaces of the discharge cell formed between the upper and lower substrates 10 and 18 and the barrier ribs 24.
For the address discharge and sustain discharge of such an AC surface discharge PDP, there is needed a high voltage above a few hundreds volts. Therefore, in order to minimize a driving power necessary for the address discharge and sustain discharge, an energy recovery apparatus is used. The energy recovery apparatus recovers a voltage between the scan electrode and the sustain electrode and uses the recovered voltage as a driving voltage during the next discharge.
Referring to FIG. 2, there is shown a conventional energy recovery apparatus of a PDP. Energy recovery circuits 30 and 32 are symmetrically connected based on a panel capacitor Cp. The panel capacitor Cp is an equivalent expression of an electrostatic capacitance formed between a scan electrode Y and a sustain electrode Z. The first energy recovery circuit 30 supplies a sustain pulse to the scan electrode Y. The second energy recovery circuit 32 supplies a sustain pulse to the sustain electrode Z while alternatively operating to the first energy recovery circuit 30.
The operation of the conventional energy recovery apparatus of the PDP will now be described with reference to the first energy recovery circuit 30. The first energy recovery circuit 30 includes an inductor L connected between the panel capacitor Cp and a source capacitor Cs, first and third switches S1 and S3 connected in parallel between the source capacitor Cs and the inductor L, and second and fourth switches S2 and S4 connected in parallel between the panel capacitor Cp and the inductor L.
The second switch S2 is connected to a sustain voltage (Vs) source, and the fourth switch S4 is connected to a ground voltage (GND) source. The source capacitor Cs charges its voltage by recovering a voltage charged at the panel capacitor Cp during the sustain discharge and re-supplies the charged voltage to the panel capacitor Cp. A voltage of Vs/2 volts corresponding to half the sustain voltage Vs is charged at the source capacitor Cs. The inductor L and the panel capacitor Cp constitute a resonant circuit. The first to fourth switches S1 to S4 control the flow of current.
Meanwhile, fifth and sixth diodes D5 and D6 connected respectively between the switch S1 and the inductor L and between the third switch S3 and the inductor L serve to prevent reverse current.
FIG. 3 illustrates timing diagrams of the switches and a waveform diagram of the panel capacitor of the first energy recovery apparatus of FIG. 2.
It is assumed that before a period T1, a voltage of 0 volts is charged at the panel capacitor Cp and a voltage of Vs/2 volts is charged at source capacitor Cs.
During a period T1, the first switch S1 is turned ON and a current path is formed through the source capacitor Cs, the fist switch S1, tire inductor L and the panel capacitor Cp. If the current path is formed, a voltage charged at the source capacitor Cs is supplied to the panel capacitor Cp. In this case, since the inductor L and the panel capacitor Cp constitute a serial resonant circuit, a voltage of Vs is charged at the panel capacitor Cp.
During a period T2, the second switch S2 is turned ON. Then the sustain voltage Vs is supplied to the scan electrode Y. The sustain voltage Vs supplied to the scan electrode Y prevents the panel capacitor Cp from being lowered below the sustain voltage Vs, thereby normally generating a sustain discharge. On the other hand, since the voltage of the panel capacitor Cp is increased up to the sustain voltage Vs during the period T1, a driving voltage supplied from the exterior in order to create the sustain discharge is minimized.
During a period T3, the first switch S1 is turned OFF. During this period T3, the scan electrode Y maintains the sustain voltage Vs.
During a period T4, the second switch S2 is turned OFF and the third switch S3 is turned ON. If the third switch S3 is turned ON, a current path is formed through the panel capacitor Cp, the inductor L, the third switch S3 and the source capacitor Cs, and a voltage charged at the panel capacitor Cp is recovered to the source capacitor Cs. Then a voltage of Vs/2 is charged at the source capacitor Cs.
During a period T5, the third switch S3 is turned OFF and the fourth switch S4 is turned ON. If the fourth switch S4 is turned ON, a current path is formed through the panel capacitor Cp and the ground voltage GND, and a voltage of the panel capacitor Cp is lowered to 0 volts. During a period T6, the state of the period T5 is maintained for a predetermined time. An AC driving pulse supplied to the scan electrode Y and sustain electrode Z is obtained by periodically repeating the periods T1 to T6.
Meanwhile, the second energy recovery circuit 32 alternatively operates to the first energy recovery circuit 30 to supply a driving voltage to the panel capacitor Cp. Therefore, sustain pulse voltages Vs with opposite polarity are supplied to the panel capacitor Cp. Consequently, a sustain discharge occurs from the discharge cells by supplying the sustain pulse voltages Vs with opposite polarity to the panel capacitor Cp.
However, the conventional energy recovery apparatus needs lots of circuit components such as switching elements because the first energy recovery circuit 30 connected to the first electrode Y and the second energy recovery circuit 32 connected to the second electrode Z operate respectively. Therefore, manufacturing cost is increased. In addition, much power is consumed due to the switching loss of a plurality of switches, such as a diode, a switching element and an inductor, on the current path.